Amphibious vehicle

ABSTRACT

An amphibious vehicle ( 32 ) having a transverse mid- or rear-mounted engine ( 12 ) arranged to drive rear road wheels ( 30 ) and/or through an axial transmission ( 37 ), a marine propulsion unit ( 38 ), in which the engine ( 12 ) is so mounted in relation to the transmission ( 37 ) to the marine propulsion unit ( 38 ) that the bottom ( 8 ) of the engine is below the axis ( 37 ) of the transmission. This ensures an advantageous metacentric height which is preferably between 370 and 180 mm.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national phase entry ofPCT/GB01/03218 with an international filing date of Jul. 19, 2001 andclaims priority from GB Patent Application Ser. No. 0017784.0, filedJul. 21, 2000.

FIELD OF THE INVENTION

The present invention relates to amphibious vehicles and moreparticularly to amphibious vehicle having increased stability on waterwhen planing in a marine mode.

BACKGROUND OF THE INVENTION

Practical amphibious vehicles generally have their engines mountedeither centrally or in the rear of the vehicle so as to ensure a ‘noseup’ attitude when under way in marine mode. One such example of thisconformation is as shown and described in Japan se Patent Publication No63-093607 (Mazda Motor Corp). This Mazda proposal is for an amphibiousvehicle having a transverse rear mounted engine arranged to driveselectively rear road wheels and/or, through an axial transmission, amarine propulsion unit in this case a pump jet. More particularly theengine is mounted at least partly above the rear road wheel drivingaxles. The pump jet is driven by a shaft from a gearbox called a“transfer device”. The transfer device is so designed to power frontroad wheels or the pump jet as required and is itself driven from theengine via a ring gear on a differential. The transfer device is mountedahead of the engine. The result of this Mazda conformation is that it isnecessary to mount the engine above the pump jet driveshaft. This shaftis in turn central to the marine pump jet, which must be mounted toprovide adequate ground clearance at the tail of the vehicle to give anadequate ramp angle when the vehicle is in road mode. Consequently thecentre of gravity of the vehicle is higher than it would be for anequivalent purely marine craft. Again because it is not possible toballast an amphibious vehicle any increase in the height of the centreof gravity relative to the centre of buoyancy is significant whenconsidering roll in marine mode for a vehicle with a low freeboard.

It is therefore an object of the present invention to reduce the heightof the centre of gravity relative to the centre of buoyancy so as toincrease the stability of the amphibious vehicle commensurate withadequate ground clearance.

SUMMARY OF THE INVENTION

Accordingly the amphibious vehicle of the invention having a transverseengine mounted in the middle or rear of the vehicle, the engine arrangedto drive rear road wheels and through an axial transmission shaftsubstantially parallel to the longitudinal axis of the vehicle, a marinepropulsion unit, is characterised in that the engine is so mounted inrelation to the transmission to the marine propulsion unit that thebottom of the engine is below the axis of the transmission shaft andwherein the vehicle has a bottom enabling planing in a marine mode.

The invention apart from assisting in ensuring “nose up” provides aconformation which is advantageous for an amphibious vehicle designed toplane.

The bottom of the hull of the vehicle is designed so as to enable thevehicle to plane. To assist this purpose the wheels may be arranged tobe stowed in a raised position in marine mode as shown in our co-pendingpatent application no WO 95/23074.

Preferably the rear wheels are driven by the engine through adifferential, a decoupler being provided between the differential and atleast one rear wheel. The marine propulsion unit is preferably driven bythe engine and road wheel transmission, preferably also through thedifferential. A further decoupler may be provided between thedifferential and the marine propulsion unit. The differential ispreferably mounted to the rear of the engine.

For an amphibious vehicle according to the invention it is preferablefor the centre of gravity to be no greater than 335 mm, and morepreferably not more than 275 mm, above the centre of buoyancy so as toensure an adequate righting moment. When it is designed to plane, theoverall planing surface of the hull of the vehicle when planing ispreferably between 1.4 and 14 m², and more preferably between 6 and 7.6m². The centre of gravity is preferably not more than 510 mm, and morepreferably not more than 450 mm, from the hull bottom.

The metacentric height, beam at vehicle waterline, and waterplane area(where the vehicle is designed to plane) are useful parameters ofvehicle stability. It is preferred that the metacentric height isbetween 370 and 180 mm, and more preferably between 370 mm and 290 mm,depending on vehicle size, load, and configuration. Furthermore, theratio of metacentric height to the beam at the vehicle waterline shouldpreferably be between 0.10 and 0.33, and more preferably between 0.14and 0.21. The ratio of metacentric height squared to planing area shouldpreferably be between 0.004 and 0.052, and more preferably between 0.007and 0.021; all of these ratios depending on vehicle size, load andconfiguration and where appropriate, whether the vehicle is indisplacement mode or planing mode.

Embodiments of the invention will now be described with reference to theaccompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side view of a first embodiment of theinvention;

FIG. 2 is a perspective view from the rear and to one side of thepowertrain of the first embodiment;

FIG. 3 is a perspective view of an alternative powertrain to that shownin FIG. 2 for a second embodiment of the invention;

FIG. 4 is a side view of tile first embodiment to show the centre ofgravity relative the centre of buoyancy with an average loading, withthe vehicle in displacement mode and wheels stowed in marine mode;

FIG. 5 is a side view similar to FIG. 4, showing the vehicle planing;

FIG. 6 is a cross section of the vehicle of FIG. 4 taken at A-A of FIG.4 showing the buoyancy curve at the same average loading, whereininternal details are omitted for clarity; and

FIGS. 7 to 9 are diagrams illustrating the dimensions listed in the datatable on page 6 of the description.

FIG. 7 is a similar view to FIG. 6, showing a transverse cross-sectionof the vehicle;

FIG. 8 is a further, simplified transverse cross-sectional view; and

FIG. 9 is an external view similar to FIG. 4, showing the vehicle indisplacement mode, and wish wheels lowered.

These three figures are self explanatory, except for the dimension X,which is the beam dimension averaged along die length of the vehicle.Clearly, the beam dimension will be smaller at the wheel arch cutoutsthan where the hull is full width.

FIG. 10 shows the smallest (132), typical (32), and largest (232) sizesof amphibious vehicle considered practical according to the conformationas claimed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1, showing the first embodiment, shows a transverse engine 12positioned towards the rear 33 of a planing amphibious vehicle 32. Theengine 12, which drives through an in-line transmission 14, is arrangedto drive either rear wheels 30 or marine propulsion unit (in this case apump jet) 38 or both via differential 16 and decouplers 34 for the rearwheels (one decoupler may suffice) and shafts . The marine propulsionunit 38 is arranged to be driven via transfer gearbox 22 powered fromdifferential 16, a further decoupler 36 and shaft 37 (FIG. 2). Althougha pump jet is shown a conventional marine screw propeller may be used.In a second embodiment shown in FIG. 3, a transverse engine 12′ ismounted at the rear of a vehicle similar to that in FIG. 1. A transferdrive 40 mounted at one end 42 of the engine 12′ provides drive to atransmission 44 positioned parallel with and adjacent to the engine 12′.This arrangement is commonly known as a “wrap around transmission”.Transmission 44 is connected to an in-line differential 46.

Driveshafts 48 which provide drive to the rear wheels (not shown),similar to the arrangement of wheels 30 in FIG. 1, are connected todecoupler(s) 50 driven from either side of the differential 46. Atransfer gearbox 52 driven from differential 46 provides drive to adecoupler 54 which drives a pump jet 56 via shaft 37′.

FIGS. 4 and 6 show the relationship between centre of buoyancy B andcentre of gravity G. As the vehicle 32 in its marine mode heels so thatwaterline WL_(D) (WL_(S) in FIG. 6) becomes water wl, the centre ofbuoyancy moves along buoyancy curve x to centre of buoyancy b. Thebuoyancy curve x is centered on metacentre M. As the centre of buoyancyshifts from B to b, a righting moment develops, so that at b a rightingmoment equivalent to dimension GZ applies to right the vehicle. It willtherefore be appreciated that the higher G is in relation to B; or asdimension BG increases; GZ will decrease. Thus by ensuring the bottom 8of the engine 12 (12′) is below the axis 35 of axial transmission shaft37 (37′), in the present embodiment BG should be no greater than 275 mmunder normal loading conditions of a full tank of fuel, a driver and onepassenger.

FIG. 4 also shows wheels 20, 30 raised in marine mode; which assistsplaning, as the wheels do not drag in the water. Note that due to therearward weight bias, waterline WL_(D) (waterline in displacement mode)is not parallel to the vehicle wheelbase; so the vehicle sits “nose up”even when static.

FIG. 5 shows the vehicle planing. WL_(F) represents the water line atthe front of the vehicle. Note that when planing, the vehicle sits onthe water, rather than in it. WL_(R) represents the water level at therear of the vehicle; as can be seen clearly in FIG. 6, a planing vehiclecreates a trough in the water by its passage. WL_(S) is the water levelin the surrounding water, to the rear of the vehicle.

In FIG. 6, it can be seen why the beam at the waterline is wider whenplaning than it is in displacement mode. Each side of the vehicle has astep 70, 72 between front and rear wheel arches, which is provided toease entry into the vehicle on land in the same fashion as side steps onfour-wheel-drive vehicles. These steps are submerged in displacementmode, when the vehicle is simply floating (FIG. 7). When the vehicle isplaning, although there is a gradation in conditions between front andrear of the vehicle, these steps are on the water line in the centrepart of the vehicle.

In practice the parameters following apply, for the vehicle shown inFIG. 1:

STATIC ON PLANE Length of Waterline 4.47 m 3.4 m Beam of Waterline 1.85m 2.0 m Waterplane Area, nominal (A_(p)) 8.3 m²  6.8 m²

By having shaft 37 (37′) above the bottom 8 of the engine, the enginecan be lower. This improves the drive angle to the rear wheels and thefollowing improvements result:

-   -   (i) improved road handling—less roll and better grip when        cornering    -   (ii) improved marine handling when planing    -   (iii) improved marine stability when in displacement mode    -   (iv) less tendency to heel when turning in marine mode    -   (v) in plane mode better lateral stability without having to        increase beam (noting that increasing the beam can increase drag        at high speed, ride hardness at high speed and roll in a seaway        all when planing)    -   (vi) in displacement mode, better lateral stability without        increase in beam; which would increase vessel cost, and reduce        the roll angle at which freeboard is exceeded and swamping        occurs; and could exceed a practical width for the automotive        road-going mode,

Further detailed parameters apply for the same embodiment but withdifferent loading conditions as follows (noting that the centre ofgravity rises by about 33 mm when wheels are raised in planing mode; andthat the centre of buoyancy is at the same longitudinal and laterallocation as the centre of gravity.):

Case 2: driver + Fuel + Loading Condition Case 1: unloaded 2Passengers + Luggage Mean beam - mm (X) 1326 1332 Beam at waterline,static - mm (X_(s)) 1830 1850 Beam at waterline, planing - mm (X_(p))N/A 2000 Deadrise - degrees (θ) 9 9 C of G above hull bottom - mm(Z_(cg)) 401 395 C of G from stern - mm (S_(cg)) 1680 1680 Draft - mm(D) 301 330 Water plane length, static - mm (L_(wp) ) 4400 4470 Smallimmersion due to tilt - mm (h) 50.0 50.2 Depth of deadrise - mm (dr)105.0 105.5 Wall immersion level-mm (dw) 196.0 224.5 Mean cross sectionarea immersed - mm² (A_(o)) 329510 369313 Centre of buoyancy height - mm(Z_(bo)) 174.9 189.7 Moments about hull base - m³ (A_(o)Z_(bo)) 0.05760.0701 Metacentric height - mm (M_(z)) 363.5 328.0 Centre of buoyancy tometacentre (BM) 589.6 533.3 Ratio of metacentric height to waterline0.199 0.178 beam, static (M_(z) / X_(s)) Ratio of metacentric height towaterline N/A 0.164 beam, planning (M_(z)/ X_(p)) Ratio of (metacentricheight) squared N/A 0.0158 to planning area (M_(z) ²/ A_(p))

From these parameters, it can be seen that for this embodiment, thecentre of gravity is not more than 450 mm from the vehicle hull bottom.Further, the metacentric height is within the range from 370 mm to 290mm, dependent on vehicle load and configuration.

The ratio of metacentric height to beam at the vehicle waterline isreadily calculated from the above data, and is found to be between 0.14and 0.21, dependent on vehicle load and for a planing vehicle withretractable wheels, on vehicle configuration, and whether it is indisplacement mode or in planing mode. This ratio is a useful indicatorof lateral stability on water, where a high ratio indicates highstability. For comparison, K. J. Rawson and E. C. Tupper, in “Basic ShipTheory” Volume 1, Section 4, give a typical value for a ship of 0.143.In the present case, is amphibious vehicle has an improved stabilityover the slip described by Rawson and Tupper.

The ratio of metacentric height squared to waterplane area isparticularly helpful for a planing vehicle, as an indication ofstability in both lateral and longitudinal axes. This ratio is readilycalculated from the above data, and is found to be between 0.009 and0.021, with identical provisos to the above; in that this ratio dependson vehicle load and for a planing vehicle with retractable wheels, onvehicle configuration, and whether it is in displacement mode or inplaning mode.

The above parameters are as mentioned above, calculated for anamphibious vehicle 32 according to FIG. 1 which is also shown as atypical amphibious vehicle according to the claims, in FIG. 10. Thesmallest amphibious vehicle considered practical according to theconformation as claimed is shown at 132 in FIG. 10. It is consideredthat its centre of gravity would be approximately 60 mm higher than forvehicle 32, and its planing area 1.4-3 m², dependent on hull design. Itsmetacentre would be some 50 mm lower than for vehicle 32, and its staticbeam at the waterline 1.2 m. The planing beam at the waterline would be0.9 m.

From these parameters, the centre of gravity for such a vehicle wouldnot be greater than 335 mm above the centre of buoyancy, and not morethan 510 mm from the bull bottom. The metacentric height will varybetween 260 mm and 180 mm; and its ratio to beam at waterline will varybetween 0.14 and 0.33. The ratio of metacentric height squared, toplaning area will vary from 0.011 to 0.052.

Similarly, the largest amphibious vehicle considered practical accordingto the conformation as claimed is shown at 232 in FIG. 10. Its centre ofgravity would be 40 mm higher than for vehicle 32, and its planing area10-14 m². Its metacentre would be at the same height as for vehicle 32.The static beam at the waterline would be 2.3 m, and the planing beam atthe waterline 2.4 m.

From these parameters the centre of gravity for such a vehicle would notbe greater than 315 mm above the centre of buoyancy, and not more than490 mm from the hull bottom. The metacentric height will vary between330 mm and 250 mm; and its ratio to beam at waterline will vary between0.10 and 0.14. The ratio of metacentric height squared, to planing areawill vary from 0.004 to 0.109.

1. An amphibious vehicle having road wheels and a transverse enginemounted in the middle or rear of the vehicle and having a crankshaftextending transversely of the vehicle, the engine arranged to drive rearroad wheels and through an axial transmission shaft substantiallyparallel to the longitudinal axis of the vehicle, a marine propulsionunit, characterised in that the engine is so mounted in relation to thetransmission to the marine propulsion unit that the bottom of the engineis below the axis of the transmission shaft and wherein the vehicle hasa bottom enabling planing in a marine mode, said road wheels arranged tobe stowed in a raised position to allow for planing during marinetravel, wherein in the raised position, the road wheels are angularlydisplaced in relation to the longitudinal axis of the vehicle relativeto their position for land travel wherein the engine is arranged only todrive the rear wheels and the propulsion unit; wherein in the marinemode, the vehicle sits nose up in the water.
 2. The vehicle of claim 1wherein the axes around which the road wheels rotate for raising andlowering are substantially parallel to the longitudinal axis of thevehicle.
 3. The vehicle of claim 1 wherein the rear wheels are driven bythe engine through a differential, a decoupler being provided between adifferential and at least one rear wheel.
 4. The vehicle of claim 1wherein the marine propulsion unit is arranged to be driven from theengine and road wheel transmission.
 5. The vehicle of claim 1 whereinthe marine propulsion unit is arranged to be driven from the engine,road wheel transmission, and a differential.
 6. The vehicle of claim 1wherein the marine propulsion unit is arranged to be driven from theengine, road wheel transmission, and a differential, via a furtherdecoupler.
 7. The vehicle of claim 1 wherein a differential is mountedto the rear of the engine.
 8. The vehicle of claim 1 having a centre ofgravity no greater than 335 mm above a centre of buoyancy.
 9. Thevehicle of claim 1 having a centre of gravity no greater than 275 mmabove the centre of buoyancy.
 10. The vehicle of claim 1 wherein thebottom has a planing surface between 1.4 and 14 m².
 11. The vehicle ofclaim 1 wherein the bottom has a planing surface between 6 and 7.6 m².12. The vehicle of claim 1 having a centre of gravity of the vehicle notmore than 510 mm above the vehicle hull bottom.
 13. The vehicle of claim1 having a centre of gravity of the vehicle not more than 450 mm abovethe vehicle hull bottom.
 14. The vehicle of claim 1 having a metacentricheight between 370 and 180 mm, dependent on vehicle size, load, andconfiguration.
 15. The vehicle of claim 1 having a metacentric heightbetween 370 and 290 mm, dependent on vehicle load and configuration. 16.The vehicle of claim 1 having a ratio of metacentric height to beam atthe vehicle waterline between 0.10 and 0.33, dependent on vehicle size,load, and configuration, and whether the vehicle is in displacement modeor in planing mode.
 17. The vehicle of claim 1 having a ratio ofmetacentric height to beam at the vehicle waterline between 0.14 and0.21, dependent on vehicle load and configuration, and whether thevehicle is in displacement mode or in planing mode.
 18. The vehicle ofclaim 1 having a ratio of metacentric height squared to waterplane areabetween 0.004 and 0.052, dependent on vehicle size, load, andconfiguration, and whether the vehicle is in displacement mode or inplaning mode.
 19. The vehicle of claim 1 having a ratio of metacentricheight squared to waterplane area is between 0.007 and 0.021, dependenton vehicle size, load, and configuration, and whether the vehicle is indisplacement mode or in planing mode.
 20. The vehicle of claim 1 whereinthe road wheels do not drag in the water when in the raised position.21. The vehicle of claim 1 wherein the centre of gravity of the vehicleis the same with the wheels in the raised position as with the wheel inthe lowered position.
 22. The vehicle of claim 1 wherein the vehiclesits nose up in a static position in the marine mode.
 23. The vehicle ofclaim 1 wherein the vehicle sits nose up in a static position in themarine mode, such that the waterline of the vehicle in a displacementmode is not parallel to a vehicle wheel base.
 24. The vehicle of claim 1wherein the vehicle sits nose up when planing.
 25. An amphibious vehiclehaving road wheels and a transverse engine having a crankshaft extendingtransversely of the vehicle, the engine arranged to drive rear roadwheels and through an axial transmission shaft substantially parallel tothe longitudinal axis of the vehicle, a marine propulsion unit; whereinsaid road wheels rotate inward in relation to the longitudinal axis ofthe vehicle when moved to a stowed position to enable planing in themarine mode; further wherein the vehicle sits nose up in a staticposition in a marine mode, such that the waterline of the vehicle in adisplacement mode is not parallel to a vehicle wheel base.
 26. Anamphibious vehicle having road wheels and a transverse engine mounted inthe middle or rear of the vehicle and having a crankshaft extendingtransversely of the vehicle, the engine arranged to drive rear roadwheels and through an axial transmission shaft substantially parallel tothe longitudinal axis of the vehicle, a marine propulsion unit,characterised in that the engine is so mounted in relation to thetransmission to the marine propulsion unit that the bottom of the engineis below the axis of the transmission shaft and wherein the vehicle hasa bottom enabling planing in a marine mode, said road wheels arranged tobe stowed in a raised position to allow for planning during marinetravel, wherein said road wheels are rotated inward in relation to thelongitudinal axis of the vehicle when moved to said raised positionwherein the engine is arranged only to drive the rear wheels and thepropulsion unit.
 27. An amphibious vehicle having road wheels, atransverse engine having a crankshaft extending transversely of thevehicle, and a wrap around transmission, the engine arranged to driverear road wheels and through an axial transmission shaft substantiallyparallel to the longitudinal axis of the vehicle, a marine propulsionunit; wherein said road wheels rotate inward toward the longitudinalaxis of the vehicle when moved to a stowed position to enable planing inthe marine mode; further wherein the vehicle sits nose up in a staticposition in a marine mode, such that the waterline of the vehicle in adisplacement mode is not parallel to a vehicle wheel base.
 28. Anamphibious vehicle having road wheels and a transverse engine mounted inthe middle or rear of the vehicle and having a crankshaft extendingtransversely of the vehicle, the engine arranged to drive rear roadwheels through a speed change gearbox and through rear wheel driveshafts and through an axial transmission shaft substantially parallel tothe longitudinal axis of the vehicle, a marine propulsion unit,characterised in that the engine is so mounted in relation to thetransmission to the marine propulsion unit that the bottom of the engineis below the axis of the transmission shaft and wherein the vehicle hasa bottom enabling planing in a marine mode, said road wheels arranged tobe stowed in a raised position to allow for planing during marinetravel, wherein in the raised position, the road wheels are angularlydisplaced in relation to the longitudinal axis of the vehicle relativeto their position for land travel wherein the engine is arranged only todrive the rear wheels and the propulsion unit; wherein the rear driveshafts are to the rear of the engine and gearbox; further wherein in themarine mode, the vehicle sits nose up in the water.
 29. An amphibiousvehicle having road wheels and a transverse engine mounted in the middleor rear of the vehicle and having a crankshaft extending transversely ofthe vehicle, the engine arranged to drive rear road wheels through aspeed change gearbox and through rear wheel drive shafts and through anaxial transmission shaft substantially parallel to the longitudinal axisof the vehicle, a marine propulsion unit, characterised in that theengine is so mounted in relation to the transmission to the marinepropulsion unit that the bottom of the engine is below the axis of thetransmission shaft and wherein the vehicle has a bottom enabling planingin a marine mode, said road wheels arranged to be stowed in a raisedposition to allow for planing during marine travel, wherein in theraised position, the road wheels are angularly displaced in relation tothe longitudinal axis of the vehicle relative to their position for landtravel wherein the engine is arranged only to drive the rear wheels andthe propulsion unit; wherein the rear drive shafts are to the rear ofthe crankshaft; further wherein in the marine mode, the vehicle sitsnose up in the water.